// if the neighbor nodes did not have the qualification
// in their type list they would have not been affected
// by the cardinality restriction. so this merges depends
// on their types
ds = ds.union( y.getDepends( qualification ), abox.doExplanation() );
ds = ds.union( z.getDepends( qualification ), abox.doExplanation() );
// if there were other merges based on the exact same cardinality
// restriction then this merge depends on them, too (we wouldn't
// have to merge these two nodes if the previous merge did not
// eliminate some other possibilities)